There have been conventionally studied surface treatment methods such as metal coating, nonmetal coating, and chemical conversion coating. So far, variously functional composite materials have been created using a matrix of a metal provided on a surface thereof with a film of another metal.
Plating is one of typical examples of the several surface treatment methods. This plating technique is widely adopted in various industries. However, such a layer of a metal or the like to be formed by plating described above is not sufficiently adhesive to a matrix thereof unless the matrix is appropriately selected. For example, silicon, which is most widely used in the fields of semiconductor, MEMS, and the like, is one of the matrices to be provided with a metal layer by plating. However, as having been pointed out, silicon generally has poor adhesion with a plated metal (Patent Document 1, for example).
As one of techniques for improving adhesion of a metal layer to silicon, there is disclosed a method of immersing a surface of polycrystalline silicon in a heated aqueous solution of sodium hydroxide (NaOH) to provide unevennesses in order to improve adhesion between the surface and a plated metal layer (see Patent Document 2). Also disclosed is a technique of forming a porous layer with use of a special substrate and filling pores in the porous layer with a plating material by displacement plating (Patent Document 3).    Non-Patent Document 1: K. Ito and one other, “Nanohole Patterned Media”, Journal FUJITSU, Fujitsu Limited, January 2007, Vol. 58, No. 1, pp. 90-98    Non-Patent Document 2: S. Yae and four others, “Electrochemistry Communications”, August 2003, Vol. 5, p. 632    Non-Patent Document 3: K. Tsujino and one other, “Electrochemica Acta”, Nov. 20, 2007, Vol. 53, p. 28    Patent Document 1: Japanese Unexamined Patent Publication No. 2004-193337    Patent Document 2: Japanese Unexamined Patent Publication No. S60-4271    Patent Document 3: Japanese Unexamined Patent Publication No. 2006-342402    Patent Document 4: Japanese Unexamined Patent Publication No. S57-105826    Patent Document 5: Japanese Unexamined Patent Publication No. H11-283829    Patent Document 6: Japanese Unexamined Patent Publication No. 2003-288712    Patent Document 7: Japanese Unexamined Patent Publication No. 2004-237429    Patent Document 8: Japanese Unexamined Patent Publication No. 2005-139376    Patent Document 9: Japanese Unexamined Patent Publication No. 2007-533983    Patent Document 10: United States Unexamined Patent Publication No. 2005/0101153